1. Field of the Invention
The present invention relates to a printing apparatus for carrying out the printing operation on a printing medium based on image information.
2. Description of the Related Art
Recently, it has been desired that a printing apparatus for outputting an image produced by a host apparatus such as a personal computer be structured to be thin in thickness and small in installation area, to accompany the miniaturization of the personal computer or a display. And, various printing apparatus have already been proposed for achieving such an object.
According to Japanese Patent No. 3,152,240, for example, a small and thin type ink jet printing apparatus is disclosed, which contemplates the portable use and is capable of carrying out the printing operation in a stable manner either in a vertical position or a horizontal position. A characteristic of this printing apparatus disclosed in this specification resides in that when it is used in the vertical position at which the installation area becomes smaller, a printing section including an ink tank and a printing head is located generally at a middle position of a housing as seen in the height direction, while a battery having a heavier weight is disposed beneath the former. As described above, since a particularly heavy part of the constituent elements is disposed in a lower portion of the apparatus body, a center of gravity of the entirety of the printing apparatus also shifts downward, whereby the stable printing is possible even in the vertical position in which the operation is usually liable to become unstable.
According to the above-mentioned structure used in the vertical position disclosed in the Japanese Patent No. 3,152,240, however, in practical use, the space saving is not achieved as expected if a paper-conveying space is taken into account, because the paper-feeding and discharging are carried out in a place extending in the horizontal direction from both sides of the printing apparatus relative to the installation plane. Also, according to the above specification, it is recommended that the printing in the vertical position is basically carried out on a stiff printing medium such as a postcard or a thick paper, while plain paper, for example, of A4 size, which is mainly used in the printing apparatus, is preferably printed in the horizontal position. As described above, the apparatus disclosed in Japanese Patent No. 3,152,240 originally conveys the printing medium in the horizontal direction but may be used in the vertical position if it must be located in a small installation area. Accordingly, although it could carry out the printing on an A4 size paper in the vertical position, it is expected in such a case that the printing medium hangs down or deforms on both sides of the printing apparatus, resulting in the unstable printing.
According to Japanese Patent Application Laying-open No. 2000-044104, a structure is disclosed, in which printing media prior to being printed and after being printed are stacked and accommodated, respectively, generally in the vertical position for lessening the installation area of the printing apparatus to save space.
Further, according to Japanese Patent Application Laying-open No. 2001-239662, a structure for saving a space is also disclosed, in which a body of a printing apparatus is used while being fixed to a stationary object such as a wall or a desk. A characteristic of the printing apparatus disclosed in the description of this patent publication is that a paper-feeding tray for storing a stack of non-printed printing media therein and a paper-discharging tray for accommodating the printed media therein are connected via a flexible conveying path. The paper-feeding tray and the paper-discharging tray are movable relative to each other so that both the trays are disposed at various relative angles in accordance with the environment in which the printing apparatus is used if space is limited.
However, the object of Japanese Patent Application Laying-open Nos. 2000-044104 and 2001-239662 is to save an installation space for the printing apparatus containing areas for accommodating the printing media both before and after being printed, respectively. Accordingly, an aspect point for realizing the space saving does not reside in the printing section itself, but in the positional relationship between the paper-feeding tray and the paper-discharging tray, and therefore, attention is hardly paid to the space saving of the printing section. Thus, since these prior art apparatuses do not exhibit their desired effect when a number of printing media are loaded on the printing apparatus, it is thought that these printing apparatuses are unsatisfactory from the standpoint of the miniaturization of a personal-use apparatus. Particularly, in one embodiment of Japanese Patent Application Laying-open No. 2000-044104, since the paper-feeding region and the paper-discharging region are arranged parallel to each other in the depth direction of the printing apparatus, a thickness of the apparatus body increases in the depth direction. In a modification of the embodiment in this patent publication, there is a structure in which the paper-feeding region and the paper-discharging region are arranged above and below the printing section, respectively. In such a case, a height of the apparatus must be twice a vertical dimension of the printing medium or more, whereby the center of gravity of the apparatus body is at a high position to cause the printing apparatus to be unstable as a whole.
Generally speaking, in the personal use environment in which the individual user usually operates the printing apparatus, it is unnecessary to always store a large amount of printing media in the apparatus body, but in most cases, it will be sufficient that only a relatively small number of printing media is replenished every time when required. Accordingly, attention for the space saving should be paid not only to the capacity of the paper-feeding tray, and the paper-discharging tray but also to the entirety of the printing section containing the paper-feeding path and the paper-discharging path. To save the space for the printing section, it is desired that the conveying direction of the printing medium is as vertical as possible to the installation plane of the printing apparatus, as well as both of the paper-feeding and the paper-discharging are carried out on the same side. In this regard, Japanese Patent Application Laying-open No. 6-171181 (1994) discloses a structure relatively suitable for space saving.
According to Japanese Patent Application Laying-open No. 6-171181 (1994), a structure of a printing apparatus is disclosed, in which a printing head is disposed inside of a conveying path for a printing medium to supply the printing medium from an upper side and deliver the same to the upper side again.
FIG. 1A is a schematic sectional view of the structure of the printing section disclosed in Japanese Patent Application Laying-open No. 6-171181 (1994) for the purpose of comparing the same with the inventive structure described later. In FIG. 1A, the printing medium is fed downward from an upper right position in the direction shown by an arrow. Thereafter, the printing medium is brought into tight contact with a reversal roller 101, and as the reversal roller 101 rotates, the conveying direction is converted upward. The printing operation is carried out on the printing medium conveyed upward by a printing head 102 disposed inside of the conveying path. Since the printing head 102 is located inside of the conveying path; i.e., between the paper-feeding path running downward and the paper-discharging path running upward, a size h of the printing head 102 is hardly relevant to an installation width W of the printing apparatus. The installation width W of the printing apparatus is determined by a total value of a diameter of the reversal roller 101 and a conveying space necessary for the feeding and discharging of the printing medium. Further, it can be said regarding the stability of the apparatus body that a structure, in which the reversal roller 101 having a relatively heavy weight is disposed at the lowermost end of the vertical type printing apparatus having a narrow installation area, is preferable.
In recent small-sized printing apparatuses, an ink jet system has been often employed as a printing system since the saving of the production cost is possible due to its relatively simple structure. In the above-mentioned Japanese Patent Application Laying-open No. 6-171181 (1994), the printing head 102 is positioned substantially just above the reversal roller 101. Accordingly, there is a risk in that if an ink droplet drops from the ink jet printing head, the reversal roller 101 may be contaminated thereby. Such contamination causes ink to be transferred to sequentially feed printing media, and deteriorates the quality of output image.
Also, since a printing plane is liable to be unstable due to the weight of the printing medium, it is desirable to apply a suitable tension to the printing medium in the vicinity of the printing plane. However, with reference to FIG. 1A again, in the above-mentioned Japanese Patent Application Laying-open No. 6-171181 (1994), part of the conveying path for the printing medium from the reversal roller 101 to the printing section extends substantially in the vertical direction with no means for supporting the printing medium to keep its vertical position. Further, since a contact area of the printing medium with the reversal roller 101 is as small as within a lower half region of the reversal roller 101, the effect of the reversal roller 101 itself and the frictional force generated between the printing medium and the reversal roller 101 are not useful for the purpose of supporting the printing medium from below.
In addition, according to the structure disclosed in the above-mentioned Japanese Patent Application Laying-open No. 6-171181 (1994), since a surface of the printing medium passing by the printing head, onto which ink is freshly adhered, is placed on another printing medium already discharged, there is a risk that the printing medium is contaminated or the printed image is deteriorated.